U.S. patent number 5,523,489 [Application Number 08/384,900] was granted by the patent office on 1996-06-04 for preparation of tetrahydroisohumulones.
This patent grant is currently assigned to Miller Brewing Company. Invention is credited to Henry Goldstein, Patrick L. Ting.
United States Patent |
5,523,489 |
Ting , et al. |
June 4, 1996 |
Preparation of tetrahydroisohumulones
Abstract
Tetrahydroisohumulones are prepared from isohumulones by
hydrogenating the isohumulones in a reaction solvent of ethanol
containing up to about 15% water in the presence of about 1 to
about 40 psig of hydrogen and a hydrogenation catalyst to form
tetrahydroisohumulones.
Inventors: |
Ting; Patrick L. (Brookfield,
WI), Goldstein; Henry (Brookfield, WI) |
Assignee: |
Miller Brewing Company
(Milwaukee, WI)
|
Family
ID: |
23519209 |
Appl.
No.: |
08/384,900 |
Filed: |
February 7, 1995 |
Current U.S.
Class: |
568/347;
568/350 |
Current CPC
Class: |
C12C
3/10 (20130101); C12C 3/12 (20130101); C12C
5/026 (20130101); C12C 9/025 (20130101) |
Current International
Class: |
C07C
45/00 (20060101); C07C 45/62 (20060101); C07C
045/62 () |
Field of
Search: |
;568/347,350 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Reamer; James H.
Attorney, Agent or Firm: Quarles & Brady
Claims
We claim:
1. A method of preparing tetrahydroisohumulones from isohumulones
which consists of dissolving the isohumulones in an ethanol
solution containing about 3% to about 15% water by weight and
having a pH of about 1 to about 7; reducing the isohumulones in the
solution in the presence of up to about 20 psig of hydrogen and a
palladium on carbon hydrogenation catalyst to form
tetrahydroisohumulones and isolating the tetrahydroisohumulones in
pure form by removing the ethanol and water by evaporation.
Description
FIELD OF THE INVENTION
The present invention relates to bittering agents for flavoring
beer and other beverages. More particularly, it relates to a method
of preparing tetrahydroisohumulones which are known bittering
agents.
DESCRIPTION OF THE PRIOR ART
Tetrahydroisohumulones are light-stable FDA-approved bittering
agents which can be used to add a hop flavor to beer. They usually
are prepared from the beta-acids (or lupulones) in hop extracts.
The hop extracts also contain alpha-acids (or humulones) but they
are not normally used to make tetrahydroisohumulones.
In the Worden et al. U.S. Pat. No. 3,552,975 a method is disclosed
employing organic solvents and lead salts to make
tetrahydroisohumulones from beta-acids. The final product is a
crude mixture from which the residues of lead can only be removed
with great difficulty. The presence of residual lead in products to
be consumed is obviously undesirable.
In the Worden U.S. Pat. No. 3,923,897 a process for preparing
tetrahydroisohumulones from beta-acids is disclosed which involves
the oxidation of desoxytetrahydrohumulones with a peracid followed
by isomerization of the resulting tetrahydrohumulones. The process
does not utilize lead salts but it is conducted in water immiscible
organic solvents and it involves cumbersome solvent changes which
increase process cost. The presence of even residual amounts of
such solvents in food products, such as beverages, is
undesirable.
In the Cowles et al. U.S. Pat. No. 4,644,084 a process is disclosed
for making tetrahydroisohumulones by treating beta-acids to form
desoxytetrahydrohumulones which are dissolved in an aqueous
alcoholic caustic solution and then oxidized with an
oxygen-containing gas in the presence of metallic ions to form the
desired tetrahydroisohumulones. The process of Cowles et al. patent
does not use undesirable organic solvents and is superior to other
known processes using beta-acids.
In the Hay U.S. Pat. No. 5,013,571 a process is disclosed for
simultaneously isomerizing and reducing alpha acids to
tetrahydroisohumulones (THIAA). The Hays patent process uses
relatively high pHs (8 to 10), significant amounts of water and
hydrogen pressures above about 50 psig. As a result, side reactions
can take place that can result in undesired products. Furthermore,
the desired tetrahydroisohumulones are not easily isolated from the
Hay reaction mixture.
It obviously would be desirable to have a simple method of making
tetrahydroisohumulones from isohumulones which did not result in
the formation of undesired products and in which it is easy to
isolate the tetrahydroisohumulones from the reaction mixture.
SUMMARY OF THE INVENTION
It is an object of the present invention to disclose a simple
method of preparing tetrahydroisohumulones from isohumulones that
does not result in the formation of undesirable products.
It is a further object to disclose a method of preparing
tetrahydroisohumulones from isohumulones in which the desired
tetrahydroisohumulones can be easily isolated in pure form.
In the inventive method, substantially pure isohumulones are
dissolved in ethanol containing about 3% to about 15% water (w/w)
having a pH of about 1 to about 7 and hydrogenated in the presence
of a suitable hydrogenation catalyst at pressures of from about 1
to about 40 psig within 2 hours to form the pure
tetrahydroisohumulones in the ethanol and water from which the
tetrahydroisohumulones can be readily isolated, if desired.
The tetrahydroisohumulones obtained by the practice of the
inventive method require no further purification and have the same
desirable properties as commercially available
tetrahydroisohumulones.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the preferred practice of the present invention, the
isohumulones are prepared from a purified alpha-acid preparation by
a process which comprises dissolving a whole CO.sub.2 hop extract,
containing the alpha-acids, beta-acids and hop oil, in aqueous
alkaline (two volumes of H.sub.2 O and one equivalent of KOH or
NaOH having a pH of about 6 to about 8.7) with stirring at about
50.degree. to about 60.degree. C.; separating the aqueous phase,
which contains substantially pure alpha-acids, from an oily phase,
which contains beta-acids and hop oil; adding to the aqueous phase,
a catalytic amount of a divalent magnesium salt, such as magnesium
sulfate; stirring and heating the mixture under reflux for about 30
to about 90 minutes to isomerize the alpha-acids; cooling the
mixture to about 85.degree. C. and adding 50% w/w sulfuric acid
with stirring; and when the temperature cools to about 70.degree.
C. isolating substantially pure isohumulones from the top layer of
the two layers which form.
In the preferred method of the invention, the isohumulones are
dissolved in ethanol containing about 10% w/w water, pH of about 1
to about 7, and hydrogenated with hydrogen in the presence of a 5%
palladium on carbon (Pd/C) hydrogenation catalyst at a pressure of
about 20 psig and a starting temperature of about 25.degree. C. to
form the desired tetrahydroisohumulones. The reaction proceeds to
completion within about 1 hour.
In addition to low temprature and pressure, the presence of acidic
water during hydrogenation is important because isohumulones are
subject to reduction of the carbonyl group at carbon 6 as well as
the desired reduction of the carbon-carbon double bonds. The former
reduction is undesirable because it produces
neotetrahydroisohumulones which are not as bitter as
tetrahydroisohumulones.
However, insufficient hydrogenation reaction time can result in
dihydroisohumulones (intermediates) which are light unstable in
beer. Therefore, the catalytic activity (water content) of Pd/C
plays an important role in control of incomplete or over-reduced
hydrogenation. Sufficient reaction time is required to eliminate
the dihydroisohumulones (incomplete light unstable products). If
reaction conditions are not precisely set, reduction to
neo-tetrahydroisohumulones and loss of bitterness occurs. Addition
of water to the solution decreases the catalytic activity with
respect to reduction which results in less over-reduced products
(neo-tetrahydroisohumulones).
The presence of large amounts of water is undesirable because it
makes it more difficult to isolate the tetrahydroisohumulones from
the reaction mixture.
The method of the present invention may be illustrated as follows:
##STR1## In which R is --CH(CH.sub.3).sub.2 ; --CH.sub.2
CH(CH.sub.3).sub.2 ; or --CHCH.sub.2 CH.sub.2 CH.sub.3.
The practice of the invention is further illustrated by the
following examples:
EXAMPLE 1
Preparation of a Pre-purified Alpha-Acid Solution
A whole CO.sub.2 hop extract is stirred at 50.degree.-60.degree. C.
with two volumes of water and one equivalent of potassium hydroxide
or sodium hydroxide per equivalent of alpha-acids for 10-15
minutes. Two layers form and after gravity separation, the aqueous
phase is cooled and filtered to remove trace amounts of beta-acids.
The aqueous phase usually consists of about 16% alpha-acids and no
beta-acids when assayed by UV.
EXAMPLE 2
Isomerization of the Alpha-Acids
A 2-liter sample of a pre-purified alpha-acid solution prepared as
described in Example 1 is added to 20 g of magnesium sulfate with
stirring, and brought to reflux for 30-90 minutes.
The solution is cooled to 85.degree. C., and 250 mL of 50% w/w
H.sub.2 SO.sub.4 is added with stirring to adjust the pH to about 1
to 2. When the temperature drops to 70.degree. C., the layers are
allowed to separate; the top layer contains 259 g of .gtoreq.90%
pure isohumulones as determined by UV and HPLC analysis. Trace
amounts of humulinic acids may be found, but no alpha-acids are
detected.
EXAMPLE 3
Hydrogenation of Isohumulones
To a solution of 50 g of isohumulones (prepared by the method of
Example 2) in 200 mL of ethanol is added 30 mL of water (15% w/w;
pH 1 to about 7) and 10.6 g of 5% Pd/C (5 g dry basis, Degussa
E-198 R/W catalyst).
The mixture is placed in a pressure autoclave, and the vessel is
purged with (3.times.50 psig) nitrogen. The vessel is then purged
with hydrogen, and the pressure is maintained at 20 psig, with
stirring (1200 rpm). The temperature rises from 25.degree. C.
initially to a maximum of 42.5.degree. C. after 13-15 minutes. The
reaction is continued for 15-20 minutes after the maximum
temperature is achieved. The reaction is complete after about 1
hour.
The catalyst is removed by suction filtration and washed with
5.0-60 mL of ethanol. Removal of the ethanol and water solvent by
rotary evaporation affords 58 g of pure tetrahydroisohumulones.
EXAMPLE 4
Formulation of Tetrahydroisohumulones
To 58 g of tetrahydroisohumulones is added 350 mL of water and it
is heated to 50.degree.-60.degree. C. with agitation. Then 17.0 g
of 45% KOH added and stirring is continued for 15-30 minutes. The
mixture is allowed to stand until it cools to room temperature. The
supernate solution is separated by decantation. The resultant
solution contains 5-10% w/w tetrahydroisohumulones which can be
added to beer.
The foregoing examples have been for purpose of illustration and a
number of changes can be made without departing from the spirit and
scope of the present invention.
The method described herein for making pure isohumulones from
alpha-acids is preferred because the other hop components
(alpha-acids, beta-acids, and hop oils) if present might be
hydrogenated to various, unacceptable products which would detract
from the usefulness and value of the tetrahydroisohumulones.
In the hydrogenation, in place of the preferred 5% palladium on
carbon catalyst, other catalysts may be used containing from about
1% by weight to about 10% palladium on carbon. The use of more
catalyst has little effect other than a shorter reaction time.
Other catalysts also might be used, such as palladium on alumina
and platinum catalysts, provided they will convert all the
isohumulones and dihydroisohumulones (intermediates) to the desired
tetrahydroisohumulones under the conditions of use without the
production of undesirable by-products or intermediates.
The pressure of the hydrogen gas employed during the hydrogenation
may be different than the 20 psig used in the Example 3.
Preferably, pressures between one atmosphere and about 40 psig are
used. However, slight increases in the overall reaction time may be
noted if lower pressures are used. The reaction time should be
sufficiently long to convert all the isohumulones and intermediates
to tetrahydroisohumulones because any residual starting material or
intermediates could render the final products (beers) unstable to
light. The reaction will usually be complete in 30 minutes to 1
hour or less even when low pressure conditions are employed. The
use of pressures higher than 40 psig increases the likelihood of
side reactions occurring which can result in the formation of
undesired products.
It will be apparent to those skilled in the art that the method of
the present invention for converting isohumulones to
tetrahydroisohumulones avoids the use of objectionable organic
solvents and other toxic reagents. The method also employs low pHs
and low pressures. Therefore, the likelihood that undesired
products will form is reduced. Furthermore, because the
tetrahydroisohumulones are obtained in a mixture of ethanol with a
relatively small amount of water, the isolation of the
tetrahydroisohumulones is facilitated.
It is intended that the invention not be limited by the foregoing
description, but only by the claims which follow:
* * * * *